Non-solid cores such as honeycomb cores have been used in aerospace applications due to their desirable structural characteristics and low weight. “Honeycomb” refers to the hexagonal structure of the material. Honeycomb materials have been made from metals and composites, and are generally sandwiched between two skins of a solid material to form the core. The skin material is attached to the honeycomb material using known fasteners including adhesives, epoxies, weld joints, and braze joints, among others. The resulting structure approximates a tessellating pattern of hexagonal prisms, where the top and bottom face of each prism is a part of the skin of solid material. Honeycomb cores are structurally strong and, due to the voids within the honeycomb portion, lightweight.
Machining of honeycomb cores has proven difficult using traditional subtractive manufacturing processes. While the finished structure is structurally strong, unfinished honeycomb cores are pliable. Especially when acted upon by forces that are not directed along the axes of individual honeycomb cells, the honeycomb may be deflected during machining. This effect is exacerbated in machining operations on cores in which not all honeycomb cells are aligned along the same axis, such as curved cores. Holding the honeycomb material in a desired form while machining is a technological challenge which has inspired numerous other inventions.
Previously known methods of holding honeycomb cores during machining involve filling portions of the honeycomb with a liquid and then freezing the liquid. The frozen liquid holds the honeycomb in place during machining, and prevents major deflections of the honeycomb material.